We have been isolating and characterizing structural gene mutations in developmentally regulated enzymes of Dictyostelium discoideum. Studies on four genes are being pursued genetically. We are also in the process of isolating mutations in regulatory genes. Such studies will shed light on the mechanism of endogenous control of temporal differentiation in higher organisms. BIBLIOGRAPHIC REFERENCES: Free, S.J., Cockburn, A., and Loomis, W.F. (1976). Alpha-Mannosidase-2: A developmentally regulated enzyme in Dictyostelium discoideum. Devel. Biol. 49:539-543. Dimond, R.L., Fransworth, P.A., and Loomis, W.F. (1976). Isolation and characterization of mutations affecting UDPG pyrophosphorylase activity in Dictyostelium discoideum. Devel. Biol. 50:169-181.